1. Field of the Invention
This invention relates to novel, biologically active derivatives of isochromans, a synthetic method for preparing isochromans and their derivatives, especially 3,7-dimethyl-8-hydroxy-6-methxoyisochroman, 3,7-dimethyl-6-hydroxy-8-methoxyisochroman and their ether and ester derivatives; and to their use as an herbicide.
2. Description of the Prior Art
Cutler et al (Agric. Biol. Chem., Volume 53 (7), 1975-1977, 1989) report that the bulk culture of Penicillium coryphilum Dierckx (ATCC accession numbers 64543 and 64869) through solid fermentation, followed by extraction, led to the isolation of 3,7-dimethyl-8-hydroxy-6-methoxyisochroman(DHMI). This metabolite inhibits growth of etiolated wheat coleoptiles. Earlier, DHMI was reported to have been isolated from moldy millet hay implicated in the death of cattle (Cox et al, J. Agric. Food Chem., Volume 27, 999, 1979), but the metabolite was not tested in plants. Because DHMI has a functional hydroxyl group at C8, the acetate and methoxy derivatives were synthesized to determine if the free hydroxyl is necessary for biological activity toward plants. Cutler et al (supra) report that the parent compound, DHMI, significantly inhibits etiolated wheat coleoptile growth by 100% and 43%, respectively at 10.sup.-3 and 10.sup.-4 M while DHMI-acetoxy inhibits it by 100% and 42%, respectively. Based on these results, the parent and two derivatives, initially obtained were assayed on greenhouse-grown bean, corn and tobacco plants. The methoxy derivative exhibited the most herbicidal activity in all plants, while the parent and acetoxy derivative were only active against corn.
Currently, DHMI is only available by fermentation of microorganisms that produce it. It would be desirable to be able to chemically synthesize DHMI and active derivatives in order to make their use as an herbicide economically feasible. The present invention provides a synthetic method for the preparation of 3,7-dimethyl-8-hydroxy-6-methoxyisochroman, the 3,7-dimethyl-6-hydroxy-8-methoxy isomer and their esters and ethers.